Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$243.47	13.336%	$275.9392	$275.94	$275.95	$275.90
Purchase #2	$10.47	3.414%	$10.8274	$10.83	$10.85	$10.80
Purchase #3	$183.37	8.580%	$199.1031	$199.10	$199.10	$199.10
Purchase #4	$96.55	13.454%	$109.5398	$109.54	$109.55	$109.50
Purchase #5	$249.30	9.830%	$273.8062	$273.81	$273.80	$273.80
Purchase #6	$145.44	12.781%	$164.0287	$164.03	$164.05	$164.00
Purchase #7	$91.26	9.513%	$99.9416	$99.94	$99.95	$99.90
7 purchase totals =	$1,019.86		$1,133.1860	$1,133.19	$1,133.25	$1,133.00